1. Field of the Invention
The present invention relates to reactive ion etching and, more particularly, to reactive ion etching using a modified reaction chamber which gives uniform silicon etching in batch processing silicon wafers.
2. Description of the Problem and the Prior Art
The clear trend in integrated circuit design is one of increasing density with a corresponding decrease in the minimum size of device features and interconnect structures. To economically fabricate devices with minimum geometric pattern sizes in a range of 1-2 microns, advanced technology manufacturing processes and tools are required. This is particularly true in the areas of pattern generation and pattern transfer to substrate material. Electron beam and X-ray lithography systems have been developed to fill the need for the generation of fine patterns in photoresist materials. However, there is a need for process technology and manufacturing capabilities which will permit transfer of the patterns to the thin substrate materials with a minimum of distortion.
The more conventional approaches, such as wet chemical and low-pressure plasma etching, are insufficient to meet the new process technology requirements for transferring fine patterns because such etching techniques are essentially isotropic processes which result in a large amount of feature undercutting. Ion milling and sputter etching provide directional etching with little undercutting but suffer the disadvantages of photoresist degradation, charge damage, low etch rates, poor selectivity and redeposition in the etched feature. Reactive ion etching, on the other hand, is a directional etching technique which does not have the disadvantages incident the use of ion milling and sputter etching.
Reactive ion etching (RIE) has been shown to be widely applicable to a variety of thin film materials and compatible with commonly utilized photoresist systems. However, one of the difficulties encountered in RIE has been obtaining etch rate uniformities suitable for manufacturing semiconductor devices. Non-uniformity of etching has been addressed in a variety of prior art etching devices. For example, U.S. Pat. No. 4,148,705 to Battey et al. describes a plasma etching reactor arrangement for etching, for example, aluminum wherein the plasma is generated between a pair of closely spaced electrodes and a distributed impedance is provided in series with the plasma to assure uniform distribution of the ionizing current and the glow discharge of the plasma throughout the region between the electrodes. In another approach, Galicki et al. describe in the IBM Technical Disclosure Bulletin, Vol. 20, No. 6, November 1977, page 2211, a plasma etch reaction chamber arrangement which provides a uniform flow of gas in the chamber.
A reactive ion etching chamber arrangement for the selective etching of silicon dioxide has been described by L. M. Ephrath in J. Electrochemical Soc.: Solid-State Science and Technology, Aug. 1979, pp. 1419-1421. Ephrath employs for the wafers an aluminum plate which is mechanically and electrically connected to a water cooled RF cathode. A grounded counterelectrode is placed in close proximity to the surface of the wafers to reduce the backscattering of aluminum.
A further plasma etch reaction chamber that attempts to achieve gas uniformity in a batch wafer processing arrangement is that described by Yamamoto et al in U.S. Pat. No. 4,151,034.
In scaling up RIE chambers to form silicon-wafer large-batch processing tools for manufacturing, etch rate uniformity becomes even more of a problem because of the larger areas involved. In such tools, the etch rate of materials like silicon can be relatively non-uniform. Typically, a non-uniformity of 35 percent has been observed in batch processing silicon wafers in a multi-wafer etching mode involving a dozen or more wafers. This nonuniformity of etch rate can occur even though the partial pressure of the injected gas, as well as the plasma density of the etching plasma, is uniform over the chamber volume. One explanation for this nonuniformity of etch rate is that although the etchant species is generated uniformly over the entire chamber volume/surface, the dominant loss occurs at the target, and thus an etchant species concentration gradient is created which leads to an enhanced etch rate at the outer edge of the target.
In accordance with the principles of the present invention, uniform etching of batches of silicon substrates is achieved in an enlarged RIE chamber by providing a mechanism within the chamber for adjusting the etchant species concentration across the target so as to be uniform. The mechanism is comprised of a plasma enhancing baffle plate (PEBP) placed in the general region above the target in such a way that it encloses a plasma volume between itself and the anode (non-target electrode). This enclosed volume is connected to the main chamber volume by providing apertures in the PEBP of various sizes, shapes and locations. The concentration of etchant species in the target region in the presence of the PEBP represents a significant increase over that with no plate. The reason for this is the increased anode area represented by the PBEP increases the RF currents and, hence, ionizing currents in the region near the PEBP. In addition, since these currents must pass through the apertures in the PEBP, they are constricted in the region of the apertures leading to a high rate of etchant species production at the aperture locations. By adjusting aperture size and location the etchant species density may be varied over the target to produce a uniform etch rate.
It is, therefore, an object of the present invention to provide an improved etching method and apparatus.
It is a further object of the present invention to provide an improved reactive ion etch apparatus.
It is yet a further object of the present invention to provide an improved silicon etching apparatus.
It is yet still a further object of the present invention to provide an improved RIE apparatus for batch etching silicon substrates.
It is another object of the present invention to provide an improved RIE apparatus for batch etching a large number of silicon substrates with etching being relatively uniform over the etching field from wafer to wafer.